In general, among the strut-type suspensions used for front wheels of four-wheeled motor vehicles and having a structure in which a strut assembly incorporating a hydraulic shock absorber in an outer cylinder integrated with a main shaft is combined with a coil spring, there is a type in which when the strut assembly rotates together with the coil spring in the steering operation, the piston rod of the strut assembly rotates, and a type in which the piston rod does not rotate. In the strut-type suspension of either type, there are cases where, a bearing is used between a mounting member on the vehicle body and an upper spring seat of the coil spring, so as to allow smooth rotation of the strut assembly.
In this bearing, a rolling bearing using balls or needles or a synthetic resin-made sliding bearing is used. However, the rolling bearing has a possibility of causing a fatigue failure in the balls or needles owing to such as infinitesimal oscillations and a vibratory load, so that there is a problem in that it is difficult to maintain a smooth steering operation. Meanwhile, the sliding bearing has a high frictional torque as compared to the rolling bearing, and therefore has the possibility of making the steering operation heavy. Furthermore, both bearings have the problem that the steering operation is made heavy due to the high frictional force of a dust seal formed of a rubber elastomer fitted to prevent the ingress of foreign objects such as dust onto sliding surfaces, and the synthetic resin-made sliding bearing in particular has the problem that the steering operation is made much heavier.